This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. This project is based on the use of the pulsed 16 GHz high resolution micro-imaging ESR spectrometer to study the distribution of trityl radical in microscopic volumes of tumor and normal mouse tissue fragments. The questions addressed in this collaboration are: 1) Is the distribution of trityl in tissue homogeneous or heterogeneous? 2) Does this assessment of heterogeneity depend on the resolution of the measurements? For example, ACERT ESR microscopy at high spin densities can reach 1 micrometer spatial resolution. For present purposes, resolution will be, initially, on the order of 50 microns progressing, depending on the trityl linewidth to 10 microns, the rough size of a single cell. Is trityl heterogeneity dependent on resolution of this order of magnitude? 3) Does the heterogeneity depend on whether or not the sample is from normal tissue or various tumors? These assessments of heterogeneities bear on the correction of trityl T2 or spin packet linewidth in that there is a moderate concentration correction. Knowledge of the heterogeneity of the trityl concentration will help to model the concentration correction within the 0.5 to 1 mm voxels in standard ESR imaging of tumor and normal tissue.